This invention relates to the collection of body fluids and to the analysis of body fluids. More specifically this invention relates to the collection of sweat and to the analysis of sweat.
The analysis of body fluids, of animals or humans, may be of value in the detection of disease, or substances, such as drugs, absorbed by a subject. Blood, saliva, urine, and sweat have all been used for such analysis. Although blood is the most commonly tested fluid, sweat probably provides the most inexpensive, safe, and convenient source of a number of analytes. Devices used to collect sweat, are commonly referred to as sweat patches.
In addition to water and electrolytes, sweat contains trace elements such as zinc, cadmium and lead. The trace elements found in sweat probably originate from blood serum. Labile metals can dissociate from proteins under the influence of the concentration gradient existing across blood capillaries, and diffuse through the capillary walls into the sweat glands.
Other substances that have been identified in sweat include: ascorbic acid, thiamine, riboflavin, nicotinic acid, amino acids, ethanol, antipyrine, creatinine, thiourea, lactate, theophylline, parathion, tetrahydrocannabinol, and insulin. Examples of disease that have been linked to the increased presence of a particular chemical in sweat include: pronounced uremia, leukaemia, and diabetes.
Typically a patch is used to collect the substance of interest, from the sweat of a person being tested. The patch is adhered to the skin of the person to be tested for a period of time, and sweat is absorbed into a fibrous pad. The pad is then analyzed for the substance.
An example of a prior art sweat patch, generally indicated by 11, is shown in FIG. 1. In addition to the storage means which comprises a fibrous pad 12, the patch comprises a semipermeable membrane 13 and a backing layer 14. The backing layer 14 is formed into a receptacle for the fibrous pad 12 and has an adhesive surface 15 for bonding the patch to the skin 16 of the patient or person being tested. The semipermeable membrane 13 separates the fibrous pad 12 from the dermal surface and may control which, and the rate at which, analytes enter the receptacle.
The design of sweat patches is a complex process. It is desirable that the environment of the skin under analysis be as little affected as possible by the presence of the patch. Sweating must occur or be made to occur in order to test the sweat. For quantitative analysis, it is desirable for the rate at which the analyte is collected to be relatively constant. The storage means used to collect the analyte should have a composition and construction such that an appropriate technique may be deployed for separation and analysis of the sweat contents. It is desirable that the storage means comprise a material that is reasonably stable when in contact with sweat.
The following documents each relate to part of the background to the present invention: U.S. Pat. No. 5,203,327; U.S. Pat. No. 4,756,314; GB 2,303,847 A; GB 2,324,866 A; and JP 10080266 A.
A number of different devices are described in U.S. Pat. No. 5,203,327. The Main theme common to these devices is the presence of a concentration zone that allows the concentration of a sweat component to be increased for testing.
The main problem addressed by U.S. Pat. No. 4,756,314 is the large variation in sweat uptake that may occur from individual to individual. The disclosure suggests that this variation may be reduced.
GB 2,303,847 A relates to bioactive silicon, resorbable silicon, and biocompatible silicon.
GB 2,324,866 A relates to an analytical device for analyzing biological materials such as blood and bile.
JP 10,080,266 A this document discloses equipment for immobilisation of a biopolymer or organism.